In the related art, ultrasonic actuators (friction drive actuators) utilizing vibration of, for example, ultrasonic waves have been used for various purposes. One example of an ultrasonic actuator vibrates, for example, a piezoelectric element with high frequency so as to drive an operation element (object) by a frictional force. Such an ultrasonic actuator is often used for driving a camera lens for focal adjustment.
Patent Literatures 1 and 2 each disclose an actuator that utilizes a traveling wave to drive a shaft (operation element) with two degrees of freedom (linear movement and rotation).